A very different Beatles had emerged by the genesis of "Strawberry Fields Forever." The Fab Four – George Harrison, John Lennon, Paul McCartney and Ringo Starr – had traded much of the mop–topped gaiety and matching-suit panache for a more bohemian consciousness. They were no longer married to the stage, but rather exploring the boundaries of studio recording, indulging creative whims as producer George Martin helped realize the band's ambitious visions. Such musical acumen came to fruition with "Strawberry Fields Forever," a song born of fantast Lennon. "Of all the Beatles recordings, 'Strawberry Fields Forever' is known for being among the most complicated and difficult to record," noted writer Mark Lewisohn in The Beatles Recording Sessions: The Official Abbey Road Studio Session Notes, 1962-1970.

Despite esoteric lyrics about a childhood haunt of Lennon's (No one I think is in my tree, I mean it must be high or low / That is you can't you know tune in but it's all right) and a beguiling arrangement, "Strawberry Fields" remains a singular pop song. It was the first song recorded for Sgt. Peppers Lonely Hearts Club Band when sessions began on November 24, 1966, following a months-long period when the group had pursued solo projects. The first session that night produced a 2:34 version of "Strawberry Fields" that bore little resemblance to the released recording that was to come, but marked the beginning of a creatively fertile exchange made possible by the lack of a looming deadline – a novelty to that point in the group's career. One of the few relations to the final version was Lennon's mellotron intro.

Recording sessions for "Strawberry Fields" continued at EMI Studios (later known as Abbey Road Studios) on November 28 and 29, as the tempo of the rhythm tracks quickened and a number of overdubs were recorded, including a new Lennon vocal track. By the end of Tuesday, November 29, the group had labeled track seven – a mix down of the rhythm track, Lennon's vocal overdub with automatic double tracking (another Abbey Road innovation) and superimposed instrumentation – as "best."

"Before the very first recording of 'Strawberry Fields Forever,' John stood opposite me in the studio and played me the song on his acoustic guitar. It was absolutely lovely," recalled Martin. "Then when we actually taped it with the usual instruments, it began to get heavy. John didn't say anything, but I knew it wasn't what he had originally wanted." At Lennon's urging, Martin set about creating a score featuring brass and string sections.

On December 8, 15 more rhythm takes were recorded, with two takes (number 15 and number 24), mixed down into one track dubbed take 25. On December 9, a series of experimental overdubs were added, including Harrison's Indian swarmandel (an Indian zither-like instrument) parts and Starr's backwards cymbals. Days later, on December 15, Martin's score, featuring trumpets and cellos, was recorded and transformed take 25 into the reduction mix take 26. It was on to this that Lennon recorded his lead vocals on two separate tracks, famously muttering "cranberry sauce" – not, contrary to rumors, "I buried Paul" – on the second overdub. The resulting take was wildly different from its original acoustic arrangement presented less than a month earlier. Still, Lennon reportedly liked the original version and the more lushly orchestrated version in equal measure, and wanted to join the two versions. However, there was a distinct problem: they were in different keys and at different tempos. As Martin recalled of Lennon's reaction: "'Well,' he said, 'you can fix it!'" Amazingly, he did.

Together with engineer Geoff Emerick, Martin sped up the original "best" (take 7) and slowed the remixed and scored version (take 26). They then edited the desired portions of the two pieces together, decreasing the pitch of the first version. Listen closely at the 60-second mark for the edit, paying particular attention to the drums.

"Strawberry Fields Forever" was not released as originally intended, as the centerpiece of Sgt. Pepper. Manager Brian Epstein, concerned that the Beatles' extended drop from public view was damaging their marketability, asked Martin for a single. The producer had McCartney's first complete track, "Penny Lane," and "Strawberry Fields Forever." Issued in February 1967 (February 13 in the U.S.; February 17 in U.K.), it was the first new Beatles single since "Please Please Me" not to top the British charts. Worse, Engelbert Humperdinck's "Release Me" kept it out of Number One.